1. Field of the Invention
The present invention relates to a Cu alloy material of high conductivity and high strength used in a Cu alloy conductor for an electric overhead wire (a trolley wire) which transmits electric power to a train through a pantograph or the like, or in a Cu alloy conductor for a cable which is used in devices or the like, and a method of manufacturing a Cu alloy conductor using the same.
2. Background of the Related Art
In a Cu alloy conductor for an electric overhead wire (trolley wire) or a Cu alloy conductor for a cable which is used in devices or the like, a hard Cu wire of high conductivity or a Cu alloy material (a Cu alloy wire) of wear resistance and heat resistance is used. The material known as a Cu alloy material is a Cu matrix with Sn of 0.25-0.35 weight % contained (refer to Japanese Examined Patent Publication No. 59-43332), which is used as a trolley wire of a bullet train or a conventional railway line.
In recent years, the further speedup of a train has been developed. This speedup requires a higher tension of an overhead trolley wire, and the tension of the electric overhead wire tends to be increased from 1.5t to 2.0t or more. Therefore, there is a demand for a trolley wire with sufficient strength against the high tension. Moreover, a large current capacity of the trolley wire is required in a railway track having a high train-passing density (the number of trains passing in a railway track per unit length).
Additionally, a cable for an instrument is desirably a conductor of high flexibility in terms of the environment to be used, that is, a conductor of high strength. A cable for an instrument is also desirably a conductor of high electric conductivity to satisfy the demands for a lighter and smaller cable.
Therefore, a Cu alloy conductor of high strength and high electric conductivity is required as a conductor to satisfy the demands described above.
As Cu alloy conductors of high strength, there are mainly two alloys such as a solid solution-strengthening alloy and a precipitation-strengthening alloy. As the solid solution-strengthening alloy, there is a Cu—Ag alloy (a silver of high concentration), a Cu—Sn alloy, a Cu—Sn—In alloy, a Cu—Mg alloy, a Cu—Sn—Mg alloy or the like. As the precipitation-strengthening alloy there is a Cu—Zr alloy, a Cu—Cr alloy, a Cu—Cr—Zr alloy or the like.
Since each of the solid solution-strengthening alloys contains oxygen of 10 weight ppm or less (0.001 weight % or less), and is superior in elongation characteristic as well as strength, it is possible to directly manufacture a Cu alloy roughing wire which is a base material of a trolley wire from the molten Cu alloy through a continuous casting and rolling process.
In a method of manufacturing a conventional trolley wire using a solid solution-strengthening alloy, for instance, a casting material of a Cu alloy which contains Sn of 0.4-0.7 weight % is hot-rolled at a temperature equal to or lower than 700° C. to produce a rolled material. There is a method of manufacturing a trolley wire by performing a finished rolling process to the rolled material at a temperature equal to or lower than 500° C. once again and through a heat treatment process to produce a roughing wire, and then, by performing the roughing wire to a wire-drawing process (refer to Japanese Unexamined Patent Publication No. 6-240426)
In addition, as another Cu alloy capable of a continuous casting and rolling, there is a Cu—O—Sn alloy. In this alloy, Sn exists as 2-3 μm crystallized particles (SnO2) inside of the matrix thereof, and it is noted that the strength and elongation characteristics of this alloy are equivalent to those of a Cu—Sn alloy containing oxygen content of 10 ppm or less by weight. This alloy also has a stronger effect of solid solution-strengthening than an effect of precipitation strengthening or of dispersion strengthening.
As a solid solution-strengthening alloy contains more contents of solid solution-strengthening elements, the alloy can improve strength the more. However, as the electric conductivity extremely decreases with more elements contained in the alloy, it is impossible to increase the current capacity, and as a result the alloy is not appropriate for use of an electric overhead wire. In the method of manufacturing a Cu alloy according to Japanese Unexamined Patent Publication No. 6-240426, for instance, Sn content contained in the alloy is 0.4-0.7 weight %, which is a large amount, and accordingly the electric conductivity is decreased. Therefore, it is difficult to manufacture a Cu alloy conductor with strength required in a high-tension overhead wire, as well as with superior electric conductivity by the present Cu—Sn alloy.
At this point, it is assumed that an electric overhead wire of high strength and high electric conductivity is obtained by adding another element with Sn. In this case, there are problems that when a temperature of finish rolling (final rolling) is too low, for example 500° C., a rolled material is often broken in a rolling process and the appearance quality of a roughing wire is extremely low and therefore the strength of an electric overhead wire becomes extremely low.
On the contrary, a precipitation-strengthening alloy has a high degree of hardness and a high tensile strength, but in a continuous casting and rolling process, such high degree of the hardness applies excessive load to a mill roll, which does not allow a manufacture by continuous casting and rolling. This alloy can be manufactured only in a batch type by extrusion or the like. Additionally, the precipitation-strengthening alloy needs a heat treatment in order to separate a precipitation-strengthening material out in the intermediate process. The precipitation-strengthening alloy has problems with low productivity and high manufacturing cost, as compared to a solid solution-strengthening alloy which can be manufactured by a continuous casting and rolling process.
Namely there are restrictions and limitations in manufacturing a Cu alloy conductor of high strength and high electric conductivity by using a method of continuous casting and rolling, which is excellent in productivity.